Image reading devices of the type that have optimal imaging distances, include a targeting scheme of some kind for aligning the image reader to the target, to be able to position the image reading device at an optimal imaging distance from the target. Most of these techniques project a pattern onto the target from a targeting light source. An aperture and light shaping optics are often used to project a pattern onto the target as an aid to the human operator to correctly position the image reader based on the targeting pattern.
The operator moves the image reader until targeting lines or dots converge at a predefined point, which relates to the point at which an acceptable image can be acquired. An acceptable image may be defined as one that contains sufficient resolution for post-processing. With this method, if the initial operating position is not correct it may be difficult for the operator to determine which direction the device must be moved in order to get into range. Further, with this method, the operator will perceive that he can only capture an image at the predetermined distance at which the lines or dots converge, even though an acceptable image could potentially be acquired some distance before or beyond that point. Another drawback to these methods is that it is often difficult to determine which direction the device must be moved in relation to the target.
There are also techniques which use laser diodes to project a crisp, sharp pattern onto the target; however, these methods also do not provide the user with intuitive alignment information with regard to the direction to move the device to place it at the appropriate distance from the target.
The techniques described above are passive in that they provide an indication of where the unit is being aimed but do not either initiate an image capture sequence or provide indication to the operator as to when an image capture sequence should be undertaken.
U.S. Pat. No. 5,668,364, which issued to Swartz et al on Sep. 16, 1997, discloses a target finding technique which uses an ultrasonic transducer to determine an optimal working distance from the target relative to the device. The disclosed technique however, is limited to portable laser scanners, and does not disclose a use with other electro-optical devices such as bar code or image readers which use an imaging engine. Further, the invention relates to an advisory function whereby an operator hears a beep or series of beeps. The auditory notification prompts the operator to manually activate the trigger mechanism in order to begin the decode sequence.
The beeping generated by these systems may be an annoyance to other people working in close proximity to the device. Further, in environments with a significant amount of ambient noise, such as in a warehouse or manufacturing facility, it may be difficult for the operator to hear the auditory prompts.
U.S. Pat. No. 6,138,915, which issued to Danielson et al on Oct. 31, 2000, discloses an instant barcode reader, including an auto-focusing technique which uses an ultrasonic transducer to determine an optimal focal distance. The transducer drives distance measurement circuitry which controls a solenoid attached to a lens assembly. The lens is moved to achieve an optimal focal distance from the target. The method also inhibits the automatic control of the lens assembly when the target is not within an acceptable reading range of the reader. An audio-visual status system is used to provide status information to a human operator, such that a red LED is illuminated to indicate that the reader is out of range of the target, and a green LED indicates a successful image acquire has occurred. Beeps or a series of beeps are also used to indicate the status of the device. This method requires a solenoid and moveable lens assembly, making it impractical for applications where space and cost are a major consideration. Further, the audio-visual verification means does not provide the human operator with intuitive information regarding which direction to move the reader, in order to achieve an optimal reading distance from the target.
Therefore there is a need for a portable image reader with a cost effective system of targeting a symbology, wherein a practical notification is provided to enable the operator to position the reader within an optimal reading range of the target.